The thing with Endo, if they really wanted him on top of another DM, they would have got him in the moment they realised that Fabinho and Henderson were off. Get him in as the backup, the squad option, and then quietly go about getting in the first choice.
The fact that they only got him in now feels to me that whilst they may still try for a first choice, they are not certain they can get one in (availability, market value, etc.), and do not want to end up scrambling on deadline day as they did last summer.